The present invention relates generally to a new quasi-isostatic lamination apparatus and quasi-isostatic lamination method for forming semiconductor ceramic carriers or substrates (hereafter semiconductor substrates or just substrates) with isotropic density.
Semiconductor substrates and devices are becoming smaller and more dense with the evolution of new technologies. However, increases in circuit density produce a corresponding increase in overall manufacturing problems. These manufacturing problems must, however, be kept to a minimum in order for the semiconductor manufacturer to remain competitive. The semiconductor manufacturers are therefore constantly being challenged to improve the quality of their products by identifying and eliminating defects which produce defective parts or components. Whereas significant improvements are being made to eliminate systematic defects by reducing process variability, process improvements alone are not sufficient to eliminate all the random defects which affect both yield and reliability. Historically, screening techniques have been employed to improve product failure rates to acceptable levels by culling out many of these random defects.
In their desire to improve their products, the semiconductor substrate manufacturers are constantly finding new ways and new techniques to improve or provide new products. It has been found that for most applications, control of sintered substrate dimensions like camber, distortion, feature positional accuracy and overall substrate size are extremely important for post-sinter operations like chip attach and bonding/joining. For a given substrate material set or a given green sheet technology, the actual sintered dimensions may depend on substrate design, such as the amount of metal loading and metal distribution; ceramic and metal compaction and their distribution due in part to lamination pressure and pressure distribution across the substrate; and substrate thickness and sintering conditions. Usually, there is no choice available for a ceramic foundry on metal loading and distribution as well as substrate thickness. Even though the foundry has the option of altering the sintering conditions, it is extremely expensive and prohibits sintering multiple type products in a single furnace run. Lamination pressure and pressure distribution on the other hand are an extremely simple and inexpensive way of controlling the dimensions. One could make a substrate having low camber and feature distortions and then have the semiconductor device mounted on to the substrate. These semiconductor substrates with the mounted semiconductor device are often referred to as modules and are made from a plurality of ceramic layers forming an MLC (multilayer ceramic) module.
MLC modules are normally used in the electronic industry to package high performance devices (also known as integrated circuits and chips). These high performance devices have a large number of external inputs/outputs (called I/Os) such as pads or solder balls, to name a few, and these devices have a very high power dissipation. In order to accommodate such high performance devices, the MLC module also has to provide a high number of external I/Os, such as pads, pins, solder balls, to name a few, and also be able to handle the very high power dissipation that is being generated both from the module as well as the device.
The MLC substrates are typically laminated with the aid of a uniaxial hydraulic lamination press as is well known to those skilled in the art.
Hass et al. U.S. Pat. No. 5,573,622, the disclosure of which is incorporated by reference herein, discloses an apparatus for laminating substrates having cavities. In the apparatus, a compliant material (for example, a silicone gel), significantly thicker than the depth of the cavity, is applied to the top of the stack of green sheets to aid in the lamination of the stack of green sheets. Lamination is done at a low pressure of 100 to 5000 psi to avoid deforming or rounding the edges of the cavity. A compliant material with large elongation is necessary to the Hass et al. invention.
Lichti et al. U.S. Pat. No. 4,640,711, the disclosure of which is incorporated by reference herein, discloses the compressing of a body by burying it in a bed of flowable particles and applying an external pressure to the flowable particles.
Horner et al. U.S. Pat. No. 5,057,171, the disclosure of which is incorporated by reference herein, discloses an isostatic lamination press wherein an MLC substrate is placed in a liquid which is pressurized.
Strobel et al. U.S. Pat. No. 5,314,646 and Onder U.S. Pat. No. 3,797,986, the disclosures of which are incorporated by reference herein, disclose the dry pressing of powder between rigid surfaces.
One purpose of the present invention is to provide an apparatus and method that will enable better dimensional characteristics in semiconductor substrates.
Another purpose of the present invention is to provide an apparatus and method that will eliminate the need for flattening the semiconductor substrates by refiring.
Yet another purpose of the present invention is the elimination of surface machining/finishing of the semiconductor substrate for post-sinter processing.